Capped ALD films for doping fin-shaped channel regions of 3-D IC transistors

ABSTRACT

Disclosed herein are methods of doping a fin-shaped channel region of a partially fabricated 3-D transistor on a semiconductor substrate. The methods may include forming a multi-layer dopant-containing film on the substrate, forming a capping film comprising a silicon carbide material, a silicon nitride material, a silicon carbonitride material, or a combination thereof, the capping film located such that the multi-layer dopant-containing film is located in between the substrate and the capping film, and driving dopant from the dopant-containing film into the fin-shaped channel region. Multiple dopant-containing layers of the film may be formed by an atomic layer deposition process which includes adsorbing a dopant-containing film precursor such that it forms an adsorption-limited layer on the substrate and reacting adsorbed dopant-containing film precursor. Also disclosed herein are multi-station substrate processing apparatuses for doping the fin-shaped channel regions of partially fabricated 3-D transistors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claims priority to, U.S. patent application Ser. No. 13/607,386, filed Sep. 7, 2012, which is a continuation-in-part of Ser. No. 13/242,084 (issued as U.S. Pat. No. 8,637,411) filed Sep. 23, 2011, which is a continuation-in-part of Ser. No. 13/084,399 (issued as U.S. Pat. No. 8,728,956), filed Apr. 11, 2011, which claims the benefit of priority under 35 U.S.C. § 119(e) to Provisional Patent Application Nos. 61/324,710, filed Apr. 15, 2010, 61/372,367, filed Aug. 10, 2010, 61/379,081, filed Sep. 1, 2010, and 61/417,807, filed Nov. 29, 2010. U.S. patent application Ser. No. 13/242,084 is also a continuation-in-part of U.S. patent application Ser. No. 13/084,305, filed Apr. 11, 2011. U.S. patent application Ser. No. 13/607,386 also claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 61/649,114, filed May 18, 2012.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A displays a side view schematic of a traditional planar IC transistor.

FIG. 1B displays a cross-sectional view schematic of a traditional planar IC transistor.

FIG. 1C displays a perspective view schematic of a modern tri-gate IC transistor employing a fin-shaped channel region.

FIG. 1D displays another perspective view schematic of a modern tri-gate IC transistor employing a fin-shaped channel region.

FIG. 2A schematically illustrates the shadowing effect which may occur when attempting to dope the channel region of high aspect ratio fin-shaped structures via conventional ion-implantation techniques. This figure illustrates the scenario where the shadowing effect of an adjacent fin structure is increased due to the presence of deposited gate electrode material.

FIG. 2B also schematically illustrates the shadowing effect which may occur when attempting to dope the channel region of high aspect ratio fin-shaped structures via conventional ion-implantation techniques. This figure illustrates the scenario where the shadowing effect of an adjacent fin structure is increased due to the presence of a pattern mask layer.

FIG. 2C again schematically illustrates the shadowing effect which may occur when attempting to dope the channel region of high aspect ratio fin-shaped structures via conventional ion-implantation techniques. This figure illustrates the scenario where the shadowing effect of an adjacent fin structure is increased due to the presence of deposited gate electrode material and also by the presence of a pattern mask layer.

FIG. 3A schematically illustrates a dopant-containing film having a capping film.

FIG. 3B schematically illustrates the dopant-containing film of FIG. 3A disposed on a fin-shaped channel region for doping the channel region.

FIGS. 4A and 4B display schematics of a dopant-containing borosilicate glass (BSG) films sandwiched between silicon dioxide (SiO₂) layers which are used to demonstrate boron dopant diffusion through SiO₂ layers via the SIMS experiments shown in FIG. 4C.

FIG. 4C displays the results of secondary ion mass spectroscopy (SIMS) experiments which demonstrate diffusion of boron dopant through the SiO₂ of the films schematically illustrated in FIGS. 4A and 4B.

FIG. 5 displays the results of SIMS experiments demonstrating reduced diffusion of boron dopant through silicon carbide (SiC) layers sandwiching a BSG film relative to the dopant diffusion exhibited through SiO₂ exhibited in FIG. 4C.

FIG. 6A presents a flowchart schematically illustrating a method of doping a fin-shaped channel region of a partially fabricated 3-D transistor on a semiconductor substrate using a dopant-containing film and a capping film having a silicon carbide material, a silicon nitride material, a silicon carbonitride material, or a combination thereof.

FIG. 6B present a flowchart of an atomic layer deposition (ALD) process sequence for depositing a dopant-containing film.

FIG. 7 schematically illustrates a dopant-containing film similar to that illustrated in FIG. 3A but in FIG. 7 exhibiting a film structure wherein dopant-rich portions are interspersed with substantially dopant-free portions.

FIG. 8 schematically illustrates a substrate processing station suitable for performing film-forming ALD operations such as those employed in the methods disclosed herein.

FIG. 9 schematically illustrates a multi-station substrate processing tool suitable for performing film-forming ALD operations such as those employed in the methods disclosed herein.

BACKGROUND

Traditionally, integrated circuit (IC) transistors have employed a planar design wherein components of the transistor—source, drain, and channel—are formed in the surface of the semiconductor substrate, and the gate component is formed as a flat structure atop the channel region of the substrate's surface. More recently, however, the desire for smaller and smaller device sizes has motivated the development of so-called 3-D transistors wherein source, drain, and channel are formed in fin-shaped structures which extend vertically from the substrate surface, generally with a high aspect ratio. With the channel formed in these vertical fin structures, the gate component of a 3-D transistor can be made to wrap around the channel region, substantially increasing the surface area of the channel region relative to its volume exposed directly to the gate voltage.

The structural differences between planar and 3-D transistors is schematically illustrated in FIGS. 1A and 1B. FIG. 1A schematically illustrates a traditional planar IC transistor 100. On the left in the figure is a side view showing source 120, channel 130, and drain 140 formed in a silicon substrate 110, with gate 150 sitting atop channel 130 separated by gate dielectric 149. To the right in the figure is a cross-sectional view of the same transistor 100 taken from the point-of-view of the vertical dotted line (as indicated by the horizontal arrow). From both views, it is seen that gate 150 is only located adjacent to one side of channel 130 (separated by gate dielectric 149). FIG. 1B provides a simplified illustration of a modern 3-D transistor design 101 with side view (left) and cross-sectional view (right) similar to that shown in FIG. 1A for the planar transistor 100. It is seen from the side view that source 121, channel 131, and drain 141 extend vertically from the plane of the silicon substrate 110 (unlike planar transistor 100). However, the cross-sectional view in FIG. 1B (right) shows that gate 151 of 3-D transistor 101 is able to wrap around the channel region 131 from three sides (in contrast to the arrangement of the gate 150 in planar transistor 100). This wrapping of the gate around the vertical fin structure is further illustrated in FIG. 1C (again showing 3-D transistor 101 with source 121, drain 141, and gate 151, although channel 131 is obscured by the gate); and FIG. 1D illustrates how multiple 3-D transistors 101 formed from parallel vertical fin structures may be wrapped by a 3-D gate component 151. This fundamental shift in transistor architecture from planar to 3-D designs has created challenges for IC fabrication, and to optimally address these challenges new fabrication techniques must be developed.

SUMMARY

Disclosed herein are methods of doping a fin-shaped channel region of a partially fabricated 3-D transistor on a semiconductor substrate. In some embodiments, the methods include forming a dopant-containing film on the substrate, forming a capping film located such that the dopant-containing film is located in between the substrate and the capping film, and driving dopant from the dopant-containing film into the fin-shaped channel region. In certain such embodiments, the capping film includes a silicon carbide material, a silicon nitride material, a silicon carbonitride material, or a combination thereof. In certain such embodiments, multiple dopant-containing layers of the dopant-containing film are formed by an atomic layer deposition process which includes adsorbing a dopant-containing film precursor onto the substrate such that the precursor forms an adsorption-limited layer, removing at least some unadsorbed dopant-containing film precursor from the volume surrounding the adsorbed precursor, reacting adsorbed dopant-containing film precursor to form a dopant-containing layer on the substrate, removing desorbed dopant-containing film precursor and/or reaction by-product from the volume surrounding the dopant-containing layer when present after reacting the adsorbed precursor, and repeating this process sequence to form multiple dopant-containing layers of the dopant-containing film.

Also disclosed herein are dopant-containing films for doping the fin-shaped channel region of a partially fabricated 3-D transistor on a semiconductor substrate. In some embodiments, the films may include first and second dopant-rich portions, first and second substantially dopant-free portions, and a capping film including a silicon carbide material, a silicon nitride material, a silicon carbonitride material, or a combination thereof. In certain such embodiments, the first dopant-rich portion of the film may be formed by conformally depositing multiple dopant-containing layers sequentially, without intervening deposition of a substantially dopant-free layer, and the second dopant rich portion may also be formed by conformally depositing multiple dopant-containing layers sequentially, without intervening deposition of a substantially dopant-free layer. Likewise, in certain such embodiments, the first substantially dopant-free portion of the film may be formed by conformally depositing multiple substantially dopant-free layers sequentially, without intervening deposition of a dopant-containing layer, and the second substantially dopant-free portion of the film may also be formed by conformally depositing multiple substantially dopant-free layers sequentially, without intervening deposition of a dopant-containing layer. In certain such embodiments, the portions of the films may be located such that the first substantially dopant-free portion is located between the first and second dopant-rich portions, the second dopant-rich portion is located between the first and second substantially dopant-free portions, and the layer of capping film is located such that the first and second dopant-rich portions and the first and second substantially dopant-free portions are in between the substrate and the capping film.

Also disclosed herein are multi-station substrate processing apparatuses for doping the fin-shaped channel regions of partially fabricated 3-D transistors on the surfaces of multiple semiconductor substrates. In some embodiments, the apparatuses include a plurality of process stations having a substrate holder contained in one or more processing chambers, one or more valves for controlling flow of dopant-containing film precursor to the process stations, one or more valve-operated vacuum sources for removing dopant-containing film precursor from the volumes surrounding the process stations contained in the one or more processing chambers, and one or more controllers having, and/or having access to, machine-readable instructions for operating the one or more valves and one or more vacuum sources to dope the fin-shaped channel regions on the surfaces of the substrates. In some embodiments, included are instructions for forming a dopant-containing film on a substrate at a process station contained in a processing chamber, instructions for forming a capping film located such that the dopant-containing film is in between the substrate and the capping film, and instructions for driving dopant from the dopant-containing film into a fin-shaped channel region. In certain such embodiments, the capping film includes a silicon carbide material, a silicon nitride material, a silicon carbonitride material, or a combination thereof. In some embodiments, the multiple dopant-containing layers of the film are formed according to the instructions by an atomic layer deposition process including introducing a dopant-containing film precursor into the processing chamber containing the process station having the substrate holder holding the substrate, and allowing the precursor to adsorb onto the surface of the substrate such that the precursor forms an adsorption-limited layer on the substrate, removing unadsorbed dopant-containing film precursor from the volume surrounding the adsorbed precursor, reacting adsorbed dopant-containing film precursor to form a dopant-containing layer on the substrate, removing desorbed dopant-containing film precursor and/or reaction by-product from the volume surrounding the dopant-containing layer when present after reacting the adsorbed precursor, and repeating this process sequence to form multiple dopant-containing layers of the dopant-containing film.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail so as to not unnecessarily obscure the present invention. While the invention will be described in conjunction with specific detailed embodiments, it is to be understood that these specific detailed embodiments are not intended to limit the scope of the inventive concepts disclosed herein.

The semi-conductive region between source and drain in an IC transistor is referred to as the channel or the transistor's channel region. Electrical potential applied by the gate to the channel region affects its polarization and conductivity, effectively switching the transistor from ‘on’ to ‘off’ states and vice versa. Accordingly, channel conductivity and the ability to consistently adjust it via the gate are key aspects of IC transistor design and fabrication. In the fabrication of traditional planar IC transistors, ion implantation techniques are generally employed to dope the channel region and adjust its conductivity to a desired level. However, with the move to 3-D transistors having a channel region formed in a high-aspect ratio fin-shaped structure (in some cases, having a width of less than about 32 nanometers, or less than about 22 nanometers, or less than about 12 nanometers), ion implantation techniques have proven ineffective for providing uniform and controlled doping.

The difficulty with ion-implantation techniques is schematically illustrated in FIGS. 2A and 2B. FIG. 2A provides a cross-sectional view (analogous to that shown in FIG. 1B) of four fin-shaped channel regions 231, 232, 233, 234 of four 3-D transistors arranged in parallel (similar to that shown in FIG. 1D). Two of the channels 233, 234 have had gate material 251 applied to them. Schematically indicated in the figure are the possible incident angles of ion-flux which will reach the base of channels 231 and 232—clearing the adjacent vertical structure—and thus may be used to uniformly dope the side of each channel. ‘Angle 1’ in the figure shows that only a small range of incident angles will reach the base of channel 231 due to the shadowing effect of adjacent channel 232. Doping the sides of the channels obviously requires that the ion-flux have some horizontal component (so as to not just bombard the top), but the figure illustrates that if the horizontal component is too great the side of the channel will be differentially bombarded—with more ions reaching the upper portions than the lower portions. Thus, for channel 231, uniform bombardment requires that incident ion-flux angles be restricted to a range between zero and Angle 1. In practice, however, because the fin-shaped channels have a high aspect ratio and are closely spaced, Angle 1 represents a relatively narrow range of ion fluxes difficult to achieve consistently due to, for example, electromagnetic field fluctuations in the plasma generating the ions, intra-ion collisions in the collimated ion flux, etc. Angle 2, also indicated in FIG. 2A, shows that the problem is amplified for channel 232 due to the presence of gate material 251 atop adjacent channel 233. FIG. 2B illustrates that the problem is similarly amplified for channel 232 if the adjacent channel 233 is masked with a layer of resist material 255. Moreover, FIG. 2C illustrates that the problem is greatly exacerbated if adjacent channel 233 is masked with a layer of resist material 255 atop an already present layer of gate material 251—compare Angle 3 in FIG. 2C with Angle 2 in FIGS. 2A and 2B.

Accordingly, techniques other than ion-implantation are sought to achieving consistent, uniform, and cost-effective doping of fin-shaped channel regions in 3-D transistors. An approach disclosed herein is to dope high aspect-ratio vertical fin-shaped channel structures using a dopant-containing film after conformally depositing it on the vertical structure. The basic idea is illustrated in FIGS. 3A and 3B. FIG. 3A illustrates the basic structure of a dopant-containing film 310 combined with a capping film 320. FIG. 3B illustrates this film conformally deposited on a vertical fin-shaped channel structure 131. Because the film substantially conforms to the shape of the target structure, diffusive transfer of dopant from the film to the target structure, e.g. with a thermal anneal, will result in uniform doping of the target structure. Details of such conformal films including composition, techniques for depositing them, the transferring of dopant from the film to the channel structure, as well as associated apparatuses for accomplishing these operations are described in detail herein. It is also noted, more generally, that doping via conformally deposited films may also be useful for doping other types of high aspect ratio devices structures, and may be appropriately used in many scenarios where conventional ion implantation or directional doping methods are inadequate. For instance, in addition to conventional silicon-based microelectronics, other applications of conformal doping may include microelectronics and optoelectronics based on III-V semiconductors such as GaAs, and II-VI semiconductors such as HgCdTe, as well as photovoltaics, flat panel displays, and electrochromic technology.

However, although conformal doping may offer distinct advantages in terms of the potential for uniform vertical doping of the target structure (e.g., versus ion implantation techniques), in practice uniform doping, for example with boron or phosphorous, at concentrations relevant to IC transistor fabrication have proven difficult to achieve. The root of this problem has been investigated and, without being limited to a particular theory, it is thought that it stems from rapid back-diffusion of dopant out of the films before sufficient dopant can be driven into the target channel region. In other words, lack of dopant uniformity and/or sufficient concentration in the deposited conformal film due to back-diffusion appears to result in a lack of sufficient uniformity and/or concentration of dopant in the channel region.

The problem is demonstrated by the experiments illustrated in FIGS. 4A, 4B, and 4C. The experiments involve conformal deposition of boron-containing films—in particular, borosilicate glass (BSG) films—on the front and back sides of a silicon wafer. The front-side and back-side boron-containing films are illustrated in FIGS. 4A and 4B, respectively, and as shown in the figures, each includes a dopant-containing borosilicate glass film sandwiched between two silicon dioxide (SiO₂) layers. The SiO₂ film formed on the side of the BSG film opposite the silicon wafer may be referred to as a “capping layer” or “capping film,” though it should be understood that these terms do not necessarily imply that the referred to film/layer is the uppermost film/layer relative to the wafer. Instead, these terms as used herein simply imply that some dopant-containing film is located between the “capping” film/layer and the substrate. FIGS. 4A and 4B indicate that the dopant-containing films were formed via an ALD (atomic layer deposition) process and that the BSG film was deposited to a thickness about double that of the sandwiching SiO₂ films (100 versus 50 Angstroms, respectively). After deposition, the films were annealed to accelerate the rate of diffusion of boron dopant out of the BSG film and into the adjacent films and wafer substrate.

Concentrations of boron dopant and other chemical species (silicon, oxygen) were then measured by secondary ion mass spectroscopy (SIMS) using a 500 keV beam of oxygen ions (O⁺) and the results are shown in FIG. 4C. As indicated in FIG. 4C, the SIMS experiments reveal a peak in boron concentration at the edge of the top SiO₂ film adjacent to the BSG film as well as a corresponding dip in boron concentration at the adjacent edge of the BSG film, the presence of both effects resulting from back-diffusion of boron atoms out of the edge of the BSG film. FIG. 4C also shows the presence of some boron in the bottom SiO₂ layer, as well as boron and oxygen deep into the underlying silicon substrate. However, it is thought that the presence of these species in these regions is due to the so-called “knock-on effect” of the 500 keV O⁺ ion beam—essentially, that the high kinetic energy of ions in the beam has “knocked” these atoms deeper into the film and substrate—and hence these measurements are not indicate of the film and substrate compositions prior to the experiment. In any event, the boron peak in the top SiO₂ film and corresponding adjacent boron dip in the BSG film—which cannot be a result of “knock-on effect”—demonstrate the occurrence of dopant back-diffusion, and also the fact that an SiO₂ capping film does a poor job of preventing it.

As stated above, back-diffusion of dopant out of a deposited film adversely affects dopant concentration in the film and thus the film's utility as a tool for doping an underlying material in a uniform manner. However, it has been discovered that while a capping film of SiO₂ does a poor job of preventing boron-back diffusion out of a conformal dopant-containing film, capping films formed from a silicon carbide material, a silicon nitride material, a silicon carbonitride material, or a combination thereof, are substantially more effective. For example, the effects of using a silicon carbide (SiC) capping film are demonstrated by the experimental results shown in FIG. 5. FIG. 5 presents SIMS results for a boron dopant-containing film having a SiC capping film which are analogous to the SIMS results presented in FIG. 4 for a SiO₂ capping film. The structure of the SiC-capped films are the same as the films schematically illustrated in FIGS. 4A and 4B but with the substitution of SiC for SiO₂. FIG. 5 shows that the boron peak appearing in the top SiC film adjacent to the BSG film is substantially reduced relative to the boron peak at the same location in the SiO₂ film of FIG. 4, thereby confirming that a SiC capping film does a substantially better job of preventing boron back-diffusion than an equivalent capping film formed from SiO₂ material.

Accordingly, due to the advantages associated with reducing or preventing dopant back-diffusion, disclosed herein are methods of doping the channel regions of partially fabricated 3-D transistors on semiconductor substrates which include forming a capping film comprising a silicon carbide (SiC) material, a silicon nitride material (SiN), a silicon carbonitride (SiCN) material, or a combination thereof. So as to reduce or prevent dopant diffusion, the SiC/SiN/SiCN capping film is located such that at least a portion of the dopant-containing film is located in between the substrate and the capping film. In this manner, during a thermal anneal, for example, to transfer dopant to the target region of the substrate, the capping film may block diffusion of dopant out of the dopant-containing film and away from the fin-shaped channel region by 20% or more, or 30% or more, or 40% or more, or 50% or more, or 60% or more, or 70% or more, or 80% or more, or 90% or more relative to the rate of diffusion during the same thermal anneal conditions in the absence of the capping film.

Certain such methods are schematically illustrated by the flow diagram of FIG. 6A. As indicated in the figure, the methods begin with an operation 610 of forming a dopant-containing film on a substrate having multiple dopant-containing layers formed by an ALD process. The methods then proceed with an operation 620 of forming a capping film containing a silicon carbide material, a silicon nitride material, a silicon carbonitride material, or a combination thereof, wherein (as indicated above) the capping film is located such that the dopant-containing film is located in between the substrate and the capping film. Finally, the transfer of dopant to the fin-shaped channel region of the 3-D transistor occurs in an operation 630 involving driving dopant from the dopant-containing film into the channel region. A thermal anneal may be used for this purpose, for example. In some embodiments, a laser anneal, spike anneal, laser spike anneal, rapid thermal processing (RTP), rapid thermal anneal (RTA), or millisecond anneal, may be used. In many of these instances, the driving of dopant into the channel region is achieved within a “low thermal budget” by generating a high temperature, but for just a short time. In some embodiments, the dopant may be boron. In other embodiments, the dopant may be phosphorous or arsenic. Other dopant species may also be advantageously transferred to a target structure/region on a semiconductor substrate utilizing these techniques. In some sequences of IC fabrication operations, at least a portion of the dopant containing film and/or capping film may be removed after dopant is driven into the target structure/region.

As discussed above, in order to achieve a uniform dopant concentration in the target structure, it is important that the deposited dopant-containing film substantially conform to the shape of the target structure. While, in principle, any workable method of depositing a conformal dopant-containing film may potentially be used in conjunction with the foregoing channel region doping approach, the technique often referred to in the art as atomic layer deposition (ALD) has been found an effective choice.

In contrast with chemical vapor deposition (CVD) process, where activated gas phase reactions are used to deposit films, ALD processes use surface-mediated deposition reactions to deposit films on a layer-by-layer basis. For instance, in one class of ALD processes, a first film precursor (P1) is introduced in a processing chamber in the gas phase, is exposed to a substrate, and is allowed to adsorb onto the surface of the substrate (typically at a population of surface active sites). Some molecules of P1 may form a condensed phase atop the substrate surface, including chemisorbed species and physisorbed molecules of P1. The volume surrounding the substrate surface is then evacuated to remove gas phase and physisorbed P1 so that only chemisorbed species remain. A second film precursor (P2) may then be introduced into the processing chamber so that some molecules of P2 adsorb to the substrate surface. The volume surrounding the substrate within the processing chamber may again be evacuated, this time to remove unbound P2. Subsequently, energy provided to the substrate (e.g., thermal or plasma energy) activates surface reactions between the adsorbed molecules of P1 and P2, forming a film layer. Finally, the volume surrounding the substrate is again evacuated to remove unreacted P1 and/or P2 and/or reaction by-product, if present, ending a single cycle of ALD.

ALD techniques for depositing conformal films having a variety of chemistries—and also many variations on the basic ALD process sequence—are described in detail in U.S. patent application Ser. No. 13/084,399, filed Apr. 11, 2011, titled “PLASMA ACTIVATED CONFORMAL FILM DEPOSITION”, U.S. patent application Ser. No. 13/242,084, filed Sep. 23, 2011, titled “PLASMA ACTIVATED CONFORMAL DIELECTRIC FILM DEPOSITION,” now U.S. Pat. No. 8,637,411, U.S. patent application Ser. No. 13/224,240, filed Sep. 1, 2011, titled “PLASMA ACTIVATED CONFORMAL DIELECTRIC FILM DEPOSITION”, and U.S. patent application Ser. No. 13/607,386, filed Sep. 7, 2012, titled “CONFORMAL DOPING VIA PLASMA ACTIVATED ATOMIC LAYER DEPOSITION AND CONFORMAL FILM DEPOSITION”, each of which is incorporated by reference herein in its entirety for all purposes. As described in these prior applications, a basic ALD cycle for depositing a single layer of material on a substrate may include: (i) adsorbing a film precursor onto a substrate such that it forms an adsorption-limited layer, (ii) removing unadsorbed precursor from the volume surrounding the adsorbed precursor, (iii) reacting the adsorbed-precursor to form a layer of film on the substrate, and (iv) removing desorbed film precursor and/or reaction by-product from the volume surrounding the layer of film formed on the substrate. The removing in operations (ii) and (iv) may be done via purging, evacuating, pumping down to a base pressure (“pump-to-base”), etc. the volume surrounding the substrate. It is noted that this basic ALD sequence of operations (i) through (iv) doesn't necessary involve two chemiadsorbed reactive species P1 and P2 as in the example described above, nor does it even necessarily involve a second reactive species, although these possibilities/options may be employed, depending on the desired deposition chemistries involved.

Due to the adsorption-limited nature of ALD, however, a single cycle of ALD only deposits a thin film of material, and oftentimes only a single monolayer of material. For example, depending on the exposure time of the film precursor dosing operations and the sticking coefficients of the film precursors (to the substrate surface), each ALD cycle may deposit a film layer only about 0.5 to 3 Angstroms thick. Thus, the sequence of operations in a typical ALD cycle—operations (i) through (iv) just described—are generally repeated multiple times in order to form a conformal film of the desired thickness. Thus, in some embodiments, operations (i) through (iv) are repeated consecutively at least 1 time, or at least 2 times, or at least 3 times, or at least 5 times, or at least 7 times, or at least 10 times in a row. Dopant ALD film may be deposited at a rate of about or between 0.1 Å and 2.5 Å per ALD cycle, or about or between 0.2 Å and 2.0 Å per ALD cycle, or about or between 0.3 Å and 1.8 Å per ALD cycle, or about or between 0.5 Å and 1.5 Å per ALD cycle, or about or between 0.1 Å and 1.5 Å per ALD cycle, or about or between 0.2 Å and 1.0 Å per ALD cycle, or about or between 0.3 Å and 1.0 Å per ALD cycle, or about or between 0.5 Å and 1.0 Å per ALD cycle.

In some film forming chemistries, an auxiliary reactant or co-reactant—in addition to what is referred to as the “film precursor”—may also be employed. In certain such embodiments, the auxiliary reactant or co-reactant may be flowed continuously during a subset of steps (i) through (iv) or throughout each of steps (i) through (iv) as they are repeated. In some embodiments, this other reactive chemical species (auxiliary reactant, co-reactant, etc.) may be adsorbed onto the substrate surface with the film precursor prior to its reaction with the film precursor (as in the example involving precursors P1 and P2 described above), however, in other embodiments, it may react with the adsorbed film precursor as it contacts it without prior adsorption onto the surface of the substrate, per se. Also, in some embodiments, operation (iii) of reacting the adsorbed film precursor may involve contacting the adsorbed film precursor with a plasma. The plasma may provide energy to drive the film-forming reaction on the substrate surface. In certain such embodiments, the plasma may be an oxidative plasma generated in the reaction chamber with application of suitable RF power (although in some embodiments, it may be generated remotely). In other embodiments, instead of an oxidative plasma, an inert plasma may be used. The oxidizing plasma may be formed from one or more oxidants such as O₂, N₂O, or CO₂, and may optionally include one or more diluents such as Ar, N₂, or He. In one embodiment, the oxidizing plasma is formed from O₂ and Ar. A suitable inert plasma may be formed from one or more inert gases such as He or Ar. Further variations on ALD processes are described in detail in the prior patent applications just cited (and which are incorporated by reference).

Accordingly, a basic sequence of operations for forming a dopant-containing film via an ALD process is schematically illustrated by the flowchart in FIG. 6B. A shown in the figure, an ALD process for forming multiple dopant-containing layers of film on a substrate may begin with an operation 611 of adsorbing a dopant-containing film precursor onto the substrate such that the precursor forms an adsorption-limited layer on the substrate, followed by an operation 612 of removing at least some unadsorbed dopant-containing film precursor from the volume surrounding the adsorbed precursor. Thereafter, in an operation 613, the adsorbed dopant-containing film precursor is reacted to form a dopant-containing layer on the substrate, and following that, in operation 614, desorbed dopant-containing film precursor and/or reaction by-product is removed from the volume surrounding the dopant-containing layer when present after reacting the adsorbed precursor in operation 613.

The foregoing sequence of operations 611 through 614 represents once ALD cycle. However, since a single ALD cycle typically only deposits a thin layer of film, multiple ALD cycles may be repeated in sequence to form multiple layers of dopant-containing film (or, equivalently, a multi-layer dopant containing film of the desired thickness). Thus, referring again to FIG. 6B, after an ALD cycle concludes with operation 614, in operation 615, it is determined whether a sufficient number of layers of dopant-containing film have been formed (or whether a film of a sufficient thickness has been deposited), and if so, the film-forming operations conclude, whereas if not, the process sequence returns to operation 611 to begin another cycle of ALD. It is noted that FIGS. 6A and 6B may be viewed in combination as a method of doping a channel region of a 3-D transistor with operation 610 (FIG. 6A) of forming a dopant-containing film including the ALD process sequence of operations 611 through 615 (FIG. 6B).

In some embodiments, a dopant-containing film for doping the fin-shaped channel region of a partially fabricated 3-D transistor may include dopant-rich portions as well as substantially dopant-free portions (in addition to the capping film which may be dopant-free). Thus, for example, in some embodiments, a dopant-containing film may include a first dopant-rich portion formed by conformally depositing multiple dopant-containing layers sequentially, without intervening deposition of a substantially dopant-free layer, and a first substantially dopant-free portion formed by conformally depositing multiple substantially dopant-free layers sequentially, without intervening deposition of a dopant-containing layer.

Moreover, in certain such embodiments, there may be multiple dopant-rich portions and multiple substantially dopant-free portions which form a structure of alternating composition in the deposited film. One reason for doing this arises from the fact that, in some cases, it has been found that depositing dopant-containing film layers sequentially, using sequential ALD cycles, may be self-inhibiting (at least to a certain extent in some embodiments), and the growth rate may continue to drop after more and more dopant-rich layers have been deposited. For example, in one experiment, the total thickness of a B₂O₃ film deposited using sequential ALD cycles was found to not significantly change between the 50th ALD cycle and the 100th ALD cycle. As a result, in some embodiments, for some dopants, and for some dopant-containing film precursors, the quantity of dopant in an ALD-formed conformal film may not be effectively increased by sequentially depositing additional dopant-rich layers. These aspects are described in detail in U.S. patent application Ser. No. 13/607,386, filed Sep. 7, 2012, and titled “CONFORMAL DOPING VIA PLASMA ACTIVATED ATOMIC LAYER DEPOSITION AND CONFORMAL FILM DEPOSITION”, which is incorporated by reference herein in its entirety for all purposes.

Thus, it may be desirable to form dopant-containing films of alternating composition—alternating between dopant-rich and substantially dopant-free portions. Therefore, in these sorts of embodiments, a dopant-containing film may additionally include a second dopant-rich portion (also formed by conformally depositing multiple dopant-containing layers sequentially, without intervening deposition of a substantially dopant-free layer), and also a second substantially dopant-free portion of the film (again, formed by conformally depositing multiple substantially dopant-free layers sequentially, without intervening deposition of a dopant-containing layer); and these first and second, dopant-rich and substantially dopant-free portions may be arranged such that they alternate with one another by composition—e.g., the first substantially dopant-free portion is located between the first and second dopant-rich portions, the second dopant-rich portion is located between the first and second substantially dopant-free portions. In such an arrangement, the capping film may be located such that the first and second dopant-rich portions and the first and second substantially dopant-free portions are in between it and the substrate. FIG. 7 provides a schematic of one such example film 700 having dopant-rich portions 710 alternating with substantially dopant-free portions 720, and also having a SiC/SiN/SiCN capping film 730.

The dopant-rich portions of such films may be formed in multiple layers by multiple ALD cycles as described above, e.g., with respect to FIG. 6B. However, multiple ALD cycles may also be used to form multiple layers of the substantially dopant-free portions of such films, albeit using a dopant-free (instead of a dopant-containing) film precursor. Thus, for instance, in some embodiments, forming each of the first and second substantially dopant-free portions just described (e.g., see FIG. 7) may include (i) adsorbing a dopant-free film precursor onto the substrate such that the precursor forms an adsorption-limited layer, thereafter (ii) removing unadsorbed dopant-free film precursor from the volume surrounding the adsorbed precursor, then (iii) reacting the adsorbed dopant-free film precursor after removing unadsorbed precursor to form a substantially dopant-free layer on the substrate, and finally (iv) removing desorbed dopant-free film precursor and/or reaction by-product from the volume surrounding the substantially dopant-free layer when present after reacting the adsorbed precursor. As stated, multiple ALD cycles may be used to form multiple layers, and so the foregoing sequence of operations (i) through (iv) may be repeated multiple times to form multiple substantially dopant-free layers of the dopant-containing film. It is noted that, in some embodiments, these substantially dopant-free layers may include a dielectric material, and that, in certain such embodiments, the dielectric material may be SiO₂.

Further examples of conformal films having portions of alternating composition—including films used for doping an underlying target IC structure or substrate region—as well as methods of forming these films, are described in detail in: U.S. patent application Ser. No. 13/084,399, filed Apr. 11, 2011, and titled “PLASMA ACTIVATED CONFORMAL FILM DEPOSITION”; U.S. patent application Ser. No. 13/242,084, filed Sep. 23, 2011, and titled “PLASMA ACTIVATED CONFORMAL DIELECTRIC FILM DEPOSITION,” now U.S. Pat. No. 8,637,411; U.S. patent application Ser. No. 13/224,240, filed Sep. 1, 2011, and titled “PLASMA ACTIVATED CONFORMAL DIELECTRIC FILM DEPOSITION”; and U.S. patent application Ser. No. 13/607,386, filed Sep. 7, 2012, and titled “CONFORMAL DOPING VIA PLASMA ACTIVATED ATOMIC LAYER DEPOSITION AND CONFORMAL FILM DEPOSITION”; each of which is incorporated by reference herein in its entirety for all purposes.

Details Regarding the Capping Film

In some embodiments, the capping film may also be formed via an ALD process. For example, in some embodiments, multiple layers of the capping film may be deposited via the sequence of operations (i) through (iv) (just described) repeated multiple times to form multiple layers of the capping film. However, while substantially dopant-free layers of SiO₂ may be interspersed with the dopant-rich portions of the film, for the reasons described above with respect to FIGS. 4 and 5, the capping film would typically be composed of a material suitable for blocking dopant back-diffusion such as SiC, SiN, SiCN, or a combination thereof. In other embodiments, a chemical vapor deposition (CVD) process may be used to form the capping film, and in certain such embodiments, a plasma-enhanced chemical vapor deposition (PECVD) process. However, since CVD/PECVD processes proceed via gas phase reactions rather than through the formation of an adsorption-limited layer of reactants, they produce less conformal films than ALD techniques, and therefore ALD processes are generally preferred for forming the capping films described herein.

The capping film will generally have a sufficient concentration of SiC, SiN, SiCN, or combination thereof, and be formed of sufficient thickness to block back-diffusion of dopant to the desired extent feasible based on the chemistries and rates of diffusion involved. For instance, in some embodiments, the average concentration of SiC in the capping film may be between about 1 and 4 g/cm³, or between about 2 and 3 g/cm³, or between about 2.2 and 2.8 g/cm³. Likewise, in some embodiments, the average concentration of SiCN in the capping film may be between about 1 and 4 g/cm³, or between about 2 and 3 g/cm³, or between about 2.2 and 2.8 g/cm³, and, in some embodiments, the average concentration of SiN in the capping film may be between about 1 and 4 g/cm³, or between about 2 and 3 g/cm³, or between about 2.2 and 2.8 g/cm³. Finally, in some embodiments, the average combined concentration of SiC, SiN, and SiCN in the capping film may be between about 1 and 4 g/cm³, or between about 2 and 3 g/cm³, or between about 2.2 and 2.8 g/cm³.

Likewise, depending on the embodiment, a capping film may be formed having an average thicknesses of about 1, 2, 3, 5, 10, 20, 30, 40, 50, 100, 150, 200, 300, or 500 Angstroms, or the capping film corresponding to a given embodiment may have an average thickness within a range defined on the low end and high end by any pair of the aforementioned thicknesses such as, for example, a capping film may have an average thickness between about 1 and 500 Angstroms, or between about 5 and 200 Angstroms, or between about 10 and 100 Angstroms. In some embodiments, the capping film may be a substantially conformal film—such as, for example, if it is formed via an ALD process—and thus it may be of relatively consistent thickness, quantifiable, for example, by the relative standard deviation in the film's thickness. Thus, in embodiments where the capping film is substantially conformal, the relative standard deviation in its thickness may be less than about 20%, or less than about 15%, or less than about 10%, or less than about 5%, or less than about 4%, or less than about 3%, or less than about 2%, or less than about 1%, or even less than about 0.1%.

ALD Process Conditions

ALD processes for forming the dopant-containing films and/or capping films may be performed at various temperatures. In some embodiments, suitable temperatures within an ALD reaction chamber may range from between about 25° C. and 450° C., or between about 50° C. and 300° C., or between about 20° C. and 400° C., or between about 200° C. and 400° C., or between about 100° C. and 350° C.

Likewise, ALD processes for forming the dopant-containing films and/or capping films may be performed at various ALD reaction chamber pressures. In some embodiments, suitable pressures within the reaction chamber may range from between about 10 mTorr and 10 Torr, or between about 20 mTorr and 8 Torr, or between about 50 mTorr and 5 Torr, or between about 100 mTorr and 2 Torr.

Various RF power levels may be employed to generate a plasma if used in operation (iii). In some embodiments, suitable RF power may range from between about 100 W and 10 kW, or between about 200 W and 6 kW, or between about 500 W, and 3 kW, or between about 1 kW and 2 kW.

Various dopant-containing film precursor flow rates may be employed in operation (i). In some embodiments, suitable flow rates may range from about or between 0.1 mL/min to 10 mL/min, or about or between 0.5 mL/min and 5 mL/min, or about or between 1 mL/min and 3 mL/min.

Various gas flow rates may be used in the various operations. In some embodiments, general gas flow rates may range from about or between 1 L/min and 20 L/min, or about or between 2 L/min and 10 L/min. For the optional inert purge steps in operations (ii) and (iv), an employed burst flow rate may range from about or between 20 L/min and 100 L/min, or about or between 40 L/min and 60 L/min.

Once again, in some embodiments, a pump-to-base step refers to pumping the reaction chamber to a base pressure by directly exposing it to one or more vacuum pumps. In some embodiments, the base pressure may typically be only a few milliTorr (e.g., between about 1 and 20 mTorr). Furthermore, as indicated above, a pump-to-base step may or may not be accompanied by an inert purge, and thus carrier gases may or may not be flowing when one or more valves open up the conductance path to the vacuum pump.

Chemistries for Formation of Capping Films

Various film-forming chemistries may be used for forming the capping film. Capping films may preferably contain a silicon carbide (SiC) material, a silicon nitride (SiN) material, a silicon carbonitride (SiCN) material, or a combination thereof. Methods, techniques, and operations for depositing these types of films are described in detail in U.S. patent application Ser. No. 13/494,836, filed Jun. 12, 2012, titled “REMOTE PLASMA BASED DEPOSITION OF SiOC CLASS OF FILMS”; U.S. patent application Ser. No. 13/907,699, filed May 31, 2013, titled “METHOD TO OBTAIN SiC CLASS OF FILMS OF DESIRED COMPOSITION AND FILM PROPERTIES”; and U.S. patent application Ser. No. 14/062,648, titled “GROUND STATE HYDROGEN RADICAL SOURCES FOR CHEMICAL VAPOR DEPOSITION OF SILICON-CARBON-CONTAINING FILMS”; each of which is hereby incorporated by reference in its entirety and for all purposes.

Deposition of such films may utilize one or more silicon-containing film precursors which may be selected from a variety of compounds. Silicon-carbon-containing films (e.g., silicon carbides, silicon-carbon-oxides, silicon carbonitrides, and silicon-carbon-oxynitrides), for instance, may be formed using silicon-containing film precursors such as organosilicon reactants selected and supplied to provide desired composition properties, and in some cases, physical or electronic properties. Examples of suitable organo-silicon reactants/film-precursors may include silanes, alkyl silanes, siloxanes, alkoxy silanes, and amino silanes, among others.

Regarding the silanes, non-limiting examples include silane, disilane, trisilane, and higher silanes.

Regarding the alkyl silanes, these compounds include a central silicon atom with one or more alkyl groups bonded to it as well as one or more hydrogen atoms bonded to it. In certain embodiments, any one or more of the alkyl groups contain 1-5 carbon atoms. The alkyl groups may be saturated or unsaturated. In some embodiments, these alkyl groups may be used to SiC films. Non-limiting examples of alkyl silanes include dimethylsilane (2MS), trimethylsilane (3MS), tetramethylsilane (4MS), triethylsilane (TES), and pentamethyldisilamethane.

Other types of alkyl silanes can include alkylcarbosilanes, alkylaminosilanes, and alkyldisilazanes. Alkylcarbosilanes can have a branched polymeric structure with a carbon bonded to a silicon atom as well as alkyl groups bonded to a silicon atom. Examples include dimethyl trimethylsilyl methane (DTMSM) and bis-dimethylsilyl ethane (BDMSE). Alkylaminosilanes include amines with alkyl groups and bonded to a silicon atom. Examples include dimethylamino dimethylsilane (DMADMS), bis-dimethylamino methylsilane (BDMAMS), and tris-dimethylamino silane (TDMAS). In some embodiments, these alkyl silanes can form SiCN films. Alkyldisilazanes include silizanes and alkyl groups bonded to two silicon atoms. An example includes 1,1,3,3-tetramethyldisilazane (TMDSN). In some embodiments, TMDSN can form SiCN films.

Additionally, higher-order silanes may be used in place of monosilanes. An example of one such disilane from the alkyl silane class is hexamethyldisilane (HMDS). Another example of a disilane from the alkyl silane class can include pentamethyldisilane (PMDS), which can be used to form SiC films. In some embodiments, one of the silicon atoms can have a carbon-containing or alkoxy-containing group exclusively attached to it, and one of the silicon atoms can have a hydrogen atom exclusively attached to it.

Regarding the siloxanes, also possible class of organo-silicon film-precursors, in some embodiments, the siloxane may be cyclic. Cyclic siloxanes may include cyclotetrasiloxanes, such as 2,4,6,8-tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane (OMCTS), and heptamethylcyclotetrasiloxane (HMCTS). Other cyclic siloxanes may include, but are not limited to, cyclotrisiloxanes and cyclopentasiloxanes. Cyclic siloxanes are ring structures that may introduce porosity into a SiC film, with the size of the pores corresponding to the radius of the ring. For example, a cyclotetrasiloxane ring can have a radius of about 6.7 Angstroms. In some embodiments, the siloxane may have a three-dimensional or caged structure. Caged siloxanes have silicon atoms bridged to one another via oxygen atoms to form a polyhedron or any 3-D structure. An example of a caged siloxane precursor molecule is silsesquioxane. Caged siloxane structures are described in further detail in commonly owned U.S. Pat. No. 6,576,345 to Cleemput et al., which is incorporated by reference herein in its entirety for all purposes. Like the cyclic siloxanes, the caged siloxane can introduce porosity into a SiC film. In some embodiments, the porosity scale is mesoporous. In some embodiments, the siloxane may be linear. Linear siloxanes may include, but are not limited to, disiloxanes, such as pentamethyldisiloxane (PMDSO), tetramethyldisiloxane (TMDSO), and hexamethyl trisiloxane. PMDSO and TMDSO may be used to form SiOC films. The structural configuration (that is, linear, cyclic, or caged) of the siloxane may affect film porosity properties. For example, cyclic siloxanes may form microporous films having pores sized according to the cyclic ring size, and caged siloxanes may form mesoporous films.

Silicon-carbon-containing films may also include oxygen atoms (e.g., silicon-carbon-oxides and silicon-carbon-oxynitrides) and these may also be formed using siloxanes (e.g., those listed above), as well as other organosilicon reactants that include oxygen, such as the alkoxy silanes. The alkoxy silanes include a central silicon atom with one or more alkoxy groups bonded to it and one or more hydrogen atoms bonded to it. Examples include but are not limited to trimethoxysilane (TMOS), dimethoxysilane (DMOS), methoxysilane (MOS), methyldimethoxysilane (MDMOS), diethoxymethylsilane (DEMS), dimethylethoxysilane (DMES), dimethylaminomethoxysilane (DMAMES), and dimethylmethoxysilane (DMMOS). Many of these precursors may be used to form SiOC films.

Silicon-carbon-containing films may also include nitrogen atoms (e.g., silicon-carbon-nitrides and silicon-carbon-oxynitrides) and may be formed using an organosilicon reactant that includes nitrogen, such as amino silanes and silazanes. Non-limiting examples of amino silanes include 2,2-bis(dimethylamino)-4,4-dimethyl-2,4-disilapentane, 2,2,4-trimethyl-4-dimethylamino-3,4-disilapentane, dimethylaminodimethylsilane, bis(dimethylamino)methylsilane, and tris(dimethylamino)silane. 1,1,3,3-tetramethyldisilazane is a non-limiting example of a silazane. Further examples of aminosilanes are mono-, di-, tri- and tetra-aminosilane (H₃Si(NH₂)₄, H₂Si(NH₂)₂, HSi(NH₂)₃ and Si(NH₂)₄, respectively), as well as substituted mono-, di-, tri- and tetra-aminosilanes, for example, t-butylaminosilane, methylaminosilane, tert-butylsilanamine, bis(tertiarybutylamino)silane (SiH₂(NHC(CH₃)₃)₂ (BTBAS), tert-butyl silylcarbamate, SiH(CH₃)—(N(CH₃)₂)₂, SiHCl—(N(CH₃)₂)₂, (Si(CH₃)₂NH)₃ and the like. A further example of an aminosilane is trisilylamine (N(SiH₃)₃).

Furthermore, in some embodiments, a film-precursor may include multiple chemical groups combined into a single precursor. For example, a single precursor can include alkoxy, amino, and alkyl groups, such as DMADMS.

In depositing the SiC-containing film, multiple organo-silicon film precursors may be present in the process gas. For example, a siloxane and an alkyl silane may be used together, or a siloxane and an alkoxy silane may be used together. The relative proportions of the individual precursors can be chosen based on the chemical structures of precursors chosen and the application of the resulting SiC film. For example, the amount of siloxane can be greater than the amount of silane in molar percentages to produce a porous film.

For the deposition of silicon nitrides (SiN) and silicon carbonitrides (SiCN), an appropriate silicon-containing reactant/film-precursor, such as those described above, may be used in conjunction with a nitrogen-containing co-reactant. Non-limiting examples of nitrogen-containing co-reactants which may be used include ammonia, hydrazine, amines such as methylamine, dimethylamine, ethylamine, isopropylamine, t-butylamine, di-t-butylamine, cyclopropylamine, sec-butylamine, cyclobutylamine, isoamylamine, 2-methylbutan-2-amine, trimethylamine, diisopropylamine, diethylisopropylamine, di-t-butylhydrazine, as well as aromatic containing amines such as anilines, pyridines, and benzylamines. Amines may be primary, secondary, tertiary or quaternary (for example, tetraalkylammonium compounds). A nitrogen-containing co-reactant contains at least one nitrogen, but may also contain heteroatoms other than nitrogen. Thus, for example, hydroxylamine, t-butyloxycarbonyl amine, and N-t-butyl hydroxylamine are considered nitrogen-containing reactants.

Finally, for the deposition of silicon oxides (SiO_(x))—though not preferred by themselves for forming the capping film, in some embodiments, they are preferred for interspersing with dopant-rich portions of a dopant-containing film—an appropriate silicon-containing reactant/film-precursor as described above may be used in conjunction with an appropriate oxidizing reactant. Examples of oxidizing reactants include oxygen, ozone, hydrogen, nitrous oxide, carbon monoxide, mixtures thereof, etc. In one particular example, an oxide film may be deposited by an ALD process using bis(tert-butylamino)silane (BTBAS) as a silicon-containing film precursor in conjunction with oxygen or nitrous oxide serving as an oxidant, e.g. in ALD operation (iii), which may or may not, depending on the embodiment, flow continuously during delivery of the BTBAS (in ALD operation (i)).

Chemistries for Formation of Dopant-Containing Films

As described in the patent applications listed and incorporated by reference above (US patent application Ser. Nos. 13/084,399, 13/242,084, and 13/224,240), various dopant-containing film precursors may be used for forming the dopant-containing films, such as films of boron-doped silicate glass (BSG) (used as the dopant-containing film in the examples of FIGS. 4 and 5 above), phosphorous-doped silicate glass (PSG), boron phosphorus doped silicate glass (BPSG), arsenic (As) doped silicate glass (ASG), and the like. The dopant-containing films may include B₂O₃, B₂O, P₂O₅, P₂O₃, As₂O₃, As₂O₅, and the like.

One preferred dopant-containing film precursor where the dopant is boron is trimethyl borate (TMB). Other suitable boron-containing film precursors may include: other alkyl borates such as triethyl borate, triisopropyl borate, and tri-n-butyl borate, as well as trimethylboron, triethylboron, triphenylboron, tri-i-propyl borate, tri-n-amyl borate, B-tribromoborazine, tris(pentafluorophenyl)borane, and other similar boron containing compounds.

As indicated above, dopant-containing films having dopants other than boron are also feasible. Examples include gallium, phosphorous, or arsenic dopants, or other elements appropriate for doping a semiconductor substrate, such as other valence III and V elements.

Particular dopant-containing films having arsenic as the dopant may include, but are not limited to, arseno-silicate or arsenic-doped silicate glass (ASG), arsenic oxides (e.g., As₂O₃, As₂O₅), and arsenic oxyhydrides. Dopant-containing film precursors having arsenic as the dopant may include, but are not limited to, the alkylarsine, alkoxyarsine, and aminoarsine chemical families, and include, but are not limited to, the following specific compounds: arsine, triethylaresenate, trimethylarsine, triethylarsine, triphenylarsine, triphenylarsine oxide, ethylenebis(diphenylarsine), tris(dimethylamino)arsine, and As(OR)₃ where R is —CH₃ or —C₂H₅ or other alkyl groups (including saturated and unsaturated alkyl groups), and other similar arsenic containing compounds.

Particular dopant-containing films having phosphorous as the dopant may include, but are not limited to, phosphorus-doped silicate glass (PSG), and phosphorous oxides (e.g., P₂O₅, P₂O₃). Dopant-containing film precursors having phosphorous as the dopant may include, but are not limited to, triethoxyphosphine oxide, alkyl phosphates such as trimethylphosphate, trimethylphosphite, and other similar phosphorous containing compounds. Choice of dopant precursor is typically dictated by ease of integration into existing delivery systems, purity requirements, and overall cost.

In some embodiments, the dopant-containing film precursor may be used in combination with a silicon-containing film precursor or other co-reactant. Silicon-containing film precursors that may be used for this purpose include, but are not limited to, silane (SiH₄), disilane (Si₂H₆), and organo silanes such as methylsilane, ethylsilane, isopropylsilane, t-butylsilane, dimethylsilane, diethylsilane, di-t-butylsilane, allylsilane, sec-butylsilane, thexylsilane, isoamylsilane, t-butyldisilane, di-t-butyldisilane, and the like. Other silicon-containing film precursors listed above as applicable to capping-layer formation may also be used for dopant-containing film formation, depending on the embodiment.

Again, multiple ALD cycles may be repeated to build up stacks of conformal layers. In some embodiments, each layer may have substantially the same composition whereas in other embodiments, sequentially ALD deposited layers may have differing compositions, or in certain such embodiments, the composition may alternate from layer to layer or there may be a repeating sequence of layers having different compositions, as described above. Thus, depending on the embodiment, certain stack engineering concepts, such as those disclosed in the patent applications listed and incorporated by reference above (U.S. patent application Ser. Nos. 13/084,399, 13/242,084, and 13/224,240) may be used to modulate boron, phosphorus, or arsenic concentration in these films.

Apparatuses

The methods described herein may be performed with any suitable semiconductor substrate processing apparatus. A suitable apparatus includes hardware for accomplishing the process operations and a system controller having instructions for controlling process operations in accordance with the various channel doping methodologies disclosed herein. In some embodiments, the hardware may include one or more process stations included in a multi-station substrate processing tool, and a controller having (or having access to) machine-readable instructions for controlling process operations in accordance with the processing techniques disclosed herein.

Thus, in some embodiments, an apparatus suitable for doping the fin-shaped channel regions of partially fabricated 3-D transistors on the surfaces of semiconductor substrates may include a plurality of process stations each having a substrate holder contained in one or more processing chambers, one or more valves for controlling flow of dopant-containing film precursor to the process stations, and one or more valve-operated vacuum sources for removing dopant-containing film precursor from the volumes surrounding the process stations contained in the one or more processing chambers. And, such an apparatus may also include a controller having (or having access to) machine-readable instructions for operating the one or more valves and one or more vacuum sources to dope the fin-shaped channel regions on the surfaces of the substrates. Thus, in some embodiments, said instructions executed by the controller may include instructions for forming a dopant-containing film on a substrate at a process station contained in a processing chamber, wherein multiple dopant-containing layers of the film are formed by an ALD process. Thus, in certain such embodiments, said instructions executed by the controller may include instructions for performing ALD operations (i) though (iv) as described above, and instructions for repeating ALD operations (i) through (iv) multiple times to form multiple layers of dopant-containing film on the multiple substrates at the multiple process stations of the substrate processing apparatus. And, in some embodiments, instructions executed by the controller may further include instructions for forming a capping film comprising a silicon carbide material, a silicon nitride material, a silicon carbonitride material, or a combination thereof, and instructions for driving dopant from the dopant-containing film into the fin-shaped channel regions of partially-manufactured 3-D transistors on multiple substrates.

Accordingly, FIG. 8 schematically shows an embodiment of a reaction chamber process station 800. For simplicity, process station 800 is depicted as a standalone process station having a process chamber body 802 for maintaining a low-pressure environment. However, it will be appreciated that a plurality of process stations 800 may be included in a common process tool environment—e.g., within a common reaction chamber. For example, FIG. 9 depicts an embodiment of a multi-station processing tool. Further, it will be appreciated that, in some embodiments, one or more hardware parameters of process station 800, including those discussed in detail above, may be adjusted programmatically by one or more system controllers.

Process station 800 fluidly communicates with reactant delivery system 801 for delivering process gases to a distribution showerhead 806. Reactant delivery system 801 includes a mixing vessel 804 for blending and/or conditioning process gases for delivery to showerhead 806. One or more mixing vessel inlet valves 820 may control introduction of process gases to mixing vessel 804.

Some reactants may be stored in liquid form prior to vaporization and subsequent delivery to the process chamber 802. The embodiment of FIG. 8 includes a vaporization point 803 for vaporizing liquid reactant to be supplied to mixing vessel 804. In some embodiments, vaporization point 803 may be a heated liquid injection module. In some embodiments, vaporization point 803 may be a heated vaporizer. The saturated reactant vapor produced from such modules/vaporizers may condense in downstream delivery piping when adequate controls are not in place (e.g., when no helium is used in vaporizing/atomizing the liquid reactant). Exposure of incompatible gases to the condensed reactant may create small particles. These small particles may clog piping, impede valve operation, contaminate substrates, etc. Some approaches to addressing these issues involve sweeping and/or evacuating the delivery piping to remove residual reactant. However, sweeping the delivery piping may increase process station cycle time, degrading process station throughput. Thus, in some embodiments, delivery piping downstream of vaporization point 803 may be heat treated. In some examples, mixing vessel 804 may also be heat treated. In one non-limiting example, piping downstream of vaporization point 803 has an increasing temperature profile extending from approximately 100° C. to approximately 150° C. at mixing vessel 804.

As mentioned, in some embodiments the vaporization point 803 may be a heated liquid injection module (“liquid injector” for short). Such a liquid injector may inject pulses of a liquid reactant into a carrier gas stream upstream of the mixing vessel. In one scenario, a liquid injector may vaporize reactant by flashing the liquid from a higher pressure to a lower pressure. In another scenario, a liquid injector may atomize the liquid into dispersed microdroplets that are subsequently vaporized in a heated delivery pipe. It will be appreciated that smaller droplets may vaporize faster than larger droplets, reducing a delay between liquid injection and complete vaporization. Faster vaporization may reduce a length of piping downstream from vaporization point 803. In one scenario, a liquid injector may be mounted directly to mixing vessel 804. In another scenario, a liquid injector may be mounted directly to showerhead 806.

In some embodiments, a liquid flow controller (LFC) upstream of vaporization point 803 may be provided for controlling a mass flow of liquid for vaporization and delivery to process station 800. For example, the LFC may include a thermal mass flow meter (MFM) located downstream of the LFC. A plunger valve of the LFC may then be adjusted responsive to feedback control signals provided by a proportional-integral-derivative (PID) controller in electrical communication with the MFM. However, it may take one second or more to stabilize liquid flow using feedback control. This may extend a time for dosing a liquid reactant. Thus, in some embodiments, the LFC may be dynamically switched between a feedback control mode and a direct control mode. In some embodiments, the LFC may be dynamically switched from a feedback control mode to a direct control mode by disabling a sense tube of the LFC and the PID controller.

Showerhead 806 distributes process gases and/or reactants (e.g., dopant-containing film precursor) toward substrate 812 at the process station, the flow of which is controlled by one or more valves upstream from the showerhead (e.g., valves 820, 820A, 805). In the embodiment shown in FIG. 8, substrate 812 is located beneath showerhead 806, and is shown resting on a pedestal 808. It will be appreciated that showerhead 806 may have any suitable shape, and may have any suitable number and arrangement of ports for distributing processes gases to substrate 812.

In some embodiments, a microvolume 807 is located beneath showerhead 806. Performing an ALD process in a microvolume in the process station near the substrate rather than in the entire volume of a processing chamber may reduce reactant exposure and sweep times, may reduce times for altering process conditions (e.g., pressure, temperature, etc.), may limit an exposure of process station robotics to process gases, etc. Example microvolume sizes include, but are not limited to, volumes between 0.1 liter and 2 liters.

In some embodiments, pedestal 808 may be raised or lowered to expose substrate 812 to microvolume 807 and/or to vary a volume of microvolume 807. For example, in a substrate transfer phase, pedestal 808 may be lowered to allow substrate 812 to be loaded onto pedestal 808. During a deposition on substrate process phase, pedestal 808 may be raised to position substrate 812 within microvolume 807. In some embodiments, microvolume 807 may completely enclose substrate 812 as well as a portion of pedestal 808 to create a region of high flow impedance during a deposition process.

Optionally, pedestal 808 may be lowered and/or raised during portions the deposition process to modulate process pressure, reactant concentration, etc. within microvolume 807. In one scenario where process chamber body 802 remains at a base pressure during the process, lowering pedestal 808 may allow microvolume 807 to be evacuated. Example ratios of microvolume to process chamber volume include, but are not limited to, volume ratios between 1:500 and 1:10. It will be appreciated that, in some embodiments, pedestal height may be adjusted programmatically by a suitable system controller.

In another scenario, adjusting a height of pedestal 808 may allow a plasma density to be varied during plasma activation and/or treatment cycles included, for example, in an ALD or CVD process. At the conclusion of a deposition process phase, pedestal 808 may be lowered during another substrate transfer phase to allow removal of substrate 812 from pedestal 808.

While the example microvolume variations described herein refer to a height-adjustable pedestal, it will be appreciated that, in some embodiments, a position of showerhead 806 may be adjusted relative to pedestal 808 to vary a volume of microvolume 807. Further, it will be appreciated that a vertical position of pedestal 808 and/or showerhead 806 may be varied by any suitable mechanism within the scope of the present disclosure. In some embodiments, pedestal 808 may include a rotational axis for rotating an orientation of substrate 812. It will be appreciated that, in some embodiments, one or more of these example adjustments may be performed programmatically by one or more suitable system controllers having machine-readable instructions for performing all or a subset of the foregoing operations.

Returning to the embodiment shown in FIG. 8, showerhead 806 and pedestal 808 electrically communicate with RF power supply 814 and matching network 816 for powering a plasma. In some embodiments, the plasma energy may be controlled (e.g., via a system controller having appropriate machine-readable instructions) by controlling one or more of a process station pressure, a gas concentration, an RF source power, an RF source frequency, and a plasma power pulse timing. For example, RF power supply 814 and matching network 816 may be operated at any suitable power to form a plasma having a desired composition of radical species. Examples of suitable powers are included above. Likewise, RF power supply 814 may provide RF power of any suitable frequency. In some embodiments, RF power supply 814 may be configured to control high- and low-frequency RF power sources independently of one another. Example low-frequency RF frequencies may include, but are not limited to, frequencies between 50 kHz and 500 kHz. Example high-frequency RF frequencies may include, but are not limited to, frequencies between 1.8 MHz and 2.45 GHz. It will be appreciated that any suitable parameters may be modulated discretely or continuously to provide plasma energy for the surface reactions. In one non-limiting example, the plasma power may be intermittently pulsed to reduce ion bombardment with the substrate surface relative to continuously powered plasmas.

In some embodiments, the plasma may be monitored in-situ by one or more plasma monitors. In one scenario, plasma power may be monitored by one or more voltage, current sensors (e.g., VI probes). In another scenario, plasma density and/or process gas concentration may be measured by one or more optical emission spectroscopy (OES) sensors. In some embodiments, one or more plasma parameters may be programmatically adjusted based on measurements from such in-situ plasma monitors. For example, an OES sensor may be used in a feedback loop for providing programmatic control of plasma power. It will be appreciated that, in some embodiments, other monitors may be used to monitor the plasma and other process characteristics. Such monitors may include, but are not limited to, infrared (IR) monitors, acoustic monitors, and pressure transducers.

In some embodiments, the plasma may be controlled via input/output control (IOC) sequencing instructions. In one example, the instructions for setting plasma conditions for a plasma activation phase may be included in a corresponding plasma activation recipe phase of a process recipe. In some cases, process recipe phases may be sequentially arranged, so that all instructions for a process phase are executed concurrently with that process phase. In some embodiments, instructions for setting one or more plasma parameters may be included in a recipe phase preceding a plasma process phase. For example, a first recipe phase may include instructions for setting a flow rate of an inert (e.g., helium) and/or a reactant gas, instructions for setting a plasma generator to a power set point, and time delay instructions for the first recipe phase. A second, subsequent recipe phase may include instructions for enabling the plasma generator and time delay instructions for the second recipe phase. A third recipe phase may include instructions for disabling the plasma generator and time delay instructions for the third recipe phase. It will be appreciated that these recipe phases may be further subdivided and/or iterated in any suitable way within the scope of the present disclosure.

In some deposition processes, plasma strikes last on the order of a few seconds or more in duration. In certain implementations described herein, much shorter plasma strikes may be applied during a processing cycle. These may be on the order of 50 milliseconds to 1 second, with 0.25 seconds being a specific example. Such short RF plasma strikes require quick stabilization of the plasma. To accomplish this, the plasma generator may be configured such that the impedance match is preset to a particular voltage, while the frequency is allowed to float. Conventionally, high-frequency plasmas are generated at an RF frequency at about 13.56 MHz. In various embodiments disclosed herein, the frequency is allowed to float to a value that is different from this standard value. By permitting the frequency to float while fixing the impedance match to a predetermined voltage, the plasma can stabilize much more quickly, a result which may be important when using the very short plasma strikes associated with ALD cycles.

In some embodiments, pedestal 808 may be temperature controlled via heater 810. Further, in some embodiments, pressure control for process station 800 may be provided by one or more valve-operated vacuum sources such as butterfly valve 818. As shown in the embodiment of FIG. 8, butterfly valve 818 throttles a vacuum provided by a downstream vacuum pump (not shown). However, in some embodiments, pressure control of process station 800 may also be adjusted by varying a flow rate of one or more gases introduced to process station 800. In some embodiments, the one or more valve-operated vacuum sources—such as butterfly valve 818—may be used for removing dopant-containing film precursor from the volumes surrounding the process stations during the appropriate ALD operational phases.

As described above, one or more process stations may be included in a multi-station substrate processing tool. FIG. 9 schematically illustrates an example of a multi-station processing tool 900 which includes a plurality of process stations 901, 902, 903, 904 in a common low-pressure processing chamber 914. By maintaining each station in a low-pressure environment, defects caused by vacuum breaks between film deposition processes may be avoided.

As shown in FIG. 9, the multi-station processing tool 900 has an inbound load lock 922 and an outbound load lock 924, either or both of which may comprise a remote plasma source. A robot 926, at atmospheric pressure, is configured to move wafers from a cassette loaded through a pod 928 into inbound load lock 922 via an atmospheric port 920. A wafer is placed by the robot 926 on a pedestal 912 in the inbound load lock 922, the atmospheric port 920 is closed, and the load lock is pumped down. Where the inbound load lock 922 comprises a remote plasma source, the wafer may be exposed to a remote plasma treatment in the load lock prior to being introduced into a processing chamber 914. Further, the wafer also may be heated in the inbound load lock 922, for example, to remove moisture and adsorbed gases. Next, a chamber transport port 916 to processing chamber 914 is opened, and another robot (not shown) places the wafer into the processing chamber on a pedestal 918 at process station 901. While the embodiment depicted in FIG. 9 includes load locks, it will be appreciated that, in some embodiments, direct entry of a wafer substrate into a processing chamber may be provided.

The depicted processing chamber 914 shown in FIG. 9 provides four process stations, 901, 902, 903, and 904. Each station has a heated pedestal (shown at 918 for process station 901) and gas line inlets. It will be appreciated that in some embodiments, each process station may have different or multiple purposes. For example, in some embodiments, a process station may be switchable between an ALD process mode and a CVD process mode. Additionally or alternatively, in some embodiments, processing chamber 914 may include one or more matched pairs of ALD/CVD process stations. While the depicted processing chamber 914 comprises 4 process stations, it will be understood that a processing chamber according to the present disclosure may have any suitable number of stations. For example, in some embodiments, a processing chamber may have 1, or 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10, or 11, or 12, or 13, or 14, or 15, or 16, or more process stations (or a set of embodiments may be described as having a number of process stations per reaction chamber within a range defined by any pair of the foregoing values, such as having 2 to 6 process stations per reaction chamber, or 4 to 8 process stations per reaction chamber, or 8 to 16 process stations per reaction chamber, etc.).

FIG. 9 also depicts an embodiment of a wafer handling system 990 for transferring wafers within processing chamber 914. In some embodiments, wafer handling system 990 may transfer wafers between various process stations and/or between a process station and a load lock. It will be appreciated that any suitable wafer handling system may be employed. Non-limiting examples include wafer carousels and wafer handling robots.

FIG. 9 also depicts an embodiment of a system controller 950 employed to control process conditions and hardware states of process tool 900 and its process stations. System controller 950 may include one or more memory devices 956, one or more mass storage devices 954, and one or more processors 952. Processor 952 may include one or more CPUs, ASICs, general-purpose computer(s) and/or specific purpose computer(s), one or more analog and/or digital input/output connection(s), one or more stepper motor controller board(s), etc.

In some embodiments, system controller 950 controls some or all of the operations of process tool 900 including the operations of its individual process stations. System controller 950 may execute machine-readable system control instructions 958 on processor 952—the system control instructions 958, in some embodiments, loaded into memory device 956 from mass storage device 954. System control instructions 958 may include instructions for controlling the timing, mixture of gaseous and liquid reactants, chamber and/or station pressure, chamber and/or station temperature, wafer temperature, target power levels, RF power levels, RF exposure time, substrate pedestal, chuck, and/or susceptor position, and other parameters of a particular process performed by process tool 900. These processes may include various types of processes including, but not limited to, processes related to deposition of film on substrates. System control instructions 958 may be configured in any suitable way. For example, various process tool component subroutines or control objects may be written to control operation of the process tool components necessary to carry out various process tool processes. System control instructions 958 may be coded in any suitable computer readable programming language. In some embodiments, system control instructions 958 are implemented in software, in other embodiments, the instructions may be implemented in hardware—for example, hard-coded as logic in an ASIC (application specific integrated circuit), or, in other embodiments, implemented as a combination of software and hardware.

In some embodiments, system control software 958 may include input/output control (IOC) sequencing instructions for controlling the various parameters described above. For example, each phase of a deposition process or processes may include one or more instructions for execution by system controller 950. The instructions for setting process conditions for a dopant-containing film deposition process phase, for example, may be included in a corresponding deposition recipe phase, and likewise for a capping film deposition phase. In some embodiments, the recipe phases may be sequentially arranged, so that all instructions for a process phase are executed concurrently with that process phase.

Other computer-readable instructions and/or programs stored on mass storage device 954 and/or memory device 956 associated with system controller 950 may be employed in some embodiments. Examples of programs or sections of programs include a substrate positioning program, a process gas control program, a pressure control program, a heater control program, and a plasma control program.

A substrate positioning program may include instructions for process tool components that are used to load the substrate onto pedestal 918 and to control the spacing between the substrate and other parts of process tool 900. The positioning program may include instructions for appropriately moving substrates in and out of the reaction chamber as necessary to deposit dopant-containing and capping films on the substrates.

A process gas control program may include instructions for controlling gas composition and flow rates and optionally for flowing gas into the volumes surrounding one or more process stations prior to deposition in order to stabilize the pressure in these volumes. In some embodiments, the process gas control program may include instructions for introducing certain gases into the volume(s) surrounding the one or more process stations within a processing chamber during deposition of a dopant-containing film on a substrates, and for introducing different gases during deposition of a capping film on the substrates. The process gas control program may also include instructions to deliver these gases at the same rates, for the same durations, or at different rates and/or for different durations depending on the composition of the film being deposited. The process gas control program may also include instructions for atomizing/vaporizing a liquid reactant in the presence of helium or some other carrier gas in a heated injection module.

A pressure control program may include instructions for controlling the pressure in the process station by regulating, for example, a throttle valve in the exhaust system of the process station, a gas flow into the process station, etc. The pressure control program may include instructions for maintaining the same or different pressures during deposition of the various film types on the substrates.

A heater control program may include instructions for controlling the current to a heating unit that is used to heat the substrates. Alternatively or in addition, the heater control program may control delivery of a heat transfer gas (such as helium) to the substrate. The heater control program may include instructions for maintaining the same or different temperatures in the reaction chamber and/or volumes surrounding the process stations during deposition of the various film types on the substrates.

A plasma control program may include instructions for setting RF power levels, frequencies, and exposure times in one or more process stations in accordance with the embodiments herein. In some embodiments, the plasma control program may include instructions for using the same or different RF power levels and/or frequencies and/or exposure times during deposition of the dopant-containing film and capping film types on the substrates.

In some embodiments, there may be a user interface associated with system controller 950. The user interface may include a display screen, graphical software displays of the apparatus and/or process conditions, and user input devices such as pointing devices, keyboards, touch screens, microphones, etc.

In some embodiments, parameters adjusted by system controller 950 may relate to process conditions. Non-limiting examples include process gas compositions and flow rates, temperatures, pressures, plasma conditions (such as RF bias power levels and exposure times), etc. These parameters may be provided to the user in the form of a recipe, which may be entered utilizing the user interface.

Signals for monitoring the processes may be provided by analog and/or digital input connections of system controller 950 from various process tool sensors. The signals for controlling the processes may be output on the analog and/or digital output connections of process tool 900. Non-limiting examples of process tool sensors that may be monitored include mass flow controllers (MFCs), pressure sensors (such as manometers), thermocouples, etc. Appropriately programmed feedback and control algorithms may be used with data from these sensors to maintain process conditions.

System controller 950 may provide machine-readable instructions for implementing the above-described deposition processes. The instructions may control a variety of process parameters, such as DC power level, RF bias power level, pressure, temperature, etc. The instructions may control the parameters to operate in-situ deposition of film stacks according to various embodiments described herein.

The system controller will typically include one or more memory devices and one or more processors configured to execute machine-readable instructions so that the apparatus will perform operations in accordance with the processes disclosed herein. Machine-readable, non-transitory media containing instructions for controlling operations in accordance with the substrate doping processes disclosed herein may be coupled to the system controller.

The various apparatuses and methods described above may be used in conjunction with lithographic patterning tools and/or processes, for example, for the fabrication or manufacture of semiconductor devices, displays, LEDs, photovoltaic panels and the like. Typically, though not necessarily, such tools will be used or processes conducted together and/or contemporaneously in a common fabrication facility.

Lithographic patterning of a film typically includes some or all of the following operations, each operation enabled with a number of possible tools: (1) application of photoresist on a substrate, e.g., a substrate having a silicon nitride film formed thereon, using a spin-on or spray-on tool; (2) curing of photoresist using a hot plate or furnace or other suitable curing tool; (3) exposing the photoresist to visible or UV or x-ray light with a tool such as a wafer stepper; (4) developing the resist so as to selectively remove resist and thereby pattern it using a tool such as a wet bench or a spray developer; (5) transferring the resist pattern into an underlying film or substrate by using a dry or plasma-assisted etching tool; and (6) removing the resist using a tool such as an RF or microwave plasma resist stripper. In some embodiments, an ashable hard mask layer (such as an amorphous carbon layer) and another suitable hard mask (such as an antireflective layer) may be deposited prior to applying the photoresist.

Other Embodiments

Although the foregoing disclosed processes, methods, systems, apparatuses, and compositions have been described in detail within the context of specific embodiments for the purpose of promoting clarity and understanding, it will be apparent to one of ordinary skill in the art that there are many alternative ways of implementing these processes, methods, systems, apparatuses, and compositions which are within the spirit of this disclosure. Accordingly, the embodiments described herein are to be viewed as illustrative of the disclosed inventive concepts rather than restrictively, and are not to be used as an impermissible basis for unduly limiting the scope of any claims eventually directed to the subject matter of this disclosure. 

The invention claimed is:
 1. A method of doping a channel region of a partially fabricated transistor on a semiconductor substrate, the method comprising: (a) forming a dopant-containing film on the semiconductor substrate, wherein multiple dopant-containing layers of the dopant-containing film are formed by an atomic layer deposition process comprising: (i) adsorbing a dopant-containing film precursor onto the semiconductor substrate such that the dopant-containing film precursor forms an adsorption-limited layer on the semiconductor substrate; (ii) removing at least some unadsorbed dopant-containing film precursor from volume surrounding the adsorbed precursor; (iii) reacting adsorbed dopant-containing film precursor, after removing the at least some unadsorbed precursor in (ii), to form a dopant-containing layer on the semiconductor substrate; (iv) removing desorbed dopant-containing film precursor and/or reaction by-product from volume surrounding the dopant-containing layer when present after reacting the adsorbed precursor; and (v) repeating (i) through (iv) to form the multiple dopant-containing layers of the dopant-containing film; (b) forming a capping film comprising a silicon nitride material, the capping film located such that the dopant-containing film formed in (a) is located in between the semiconductor substrate and the capping film; and (c) driving dopant from the dopant-containing film into the channel region, wherein (a) further comprises forming multiple substantially dopant-free layers of the dopant-containing film, at least some of the substantially dopant-free layers formed by an atomic layer deposition process comprising: (vi) adsorbing a dopant-free film precursor onto the semiconductor substrate such that the dopant-free film precursor forms an adsorption-limited layer on the semiconductor substrate; (vii) removing unadsorbed dopant-free film precursor from volume surrounding the adsorbed dopant-free film precursor; (viii) reacting the adsorbed dopant-free film precursor, after removing unadsorbed dopant-free film precursor in (vii), to form a substantially dopant-free layer on the semiconductor substrate; (ix) removing desorbed dopant-free film precursor or reaction by-product or desorbed dopant-free film precursor and reaction by-product from volume surrounding the substantially dopant-free layer when present after reacting the adsorbed dopant-free film precursor; and (x) repeating (vi) through (ix) to form the multiple substantially dopant-free layers of the dopant-containing film; and wherein in (a): a first dopant-rich portion of the dopant-containing film is formed by depositing the multiple dopant-containing layers in (i) through (v) sequentially, without intervening deposition of a substantially dopant-free layer; and a first substantially dopant-free portion of the dopant-containing film is formed by depositing the multiple substantially dopant-free layers in (vi) through (x) sequentially, without intervening deposition of a dopant-containing layer.
 2. The method of claim 1, further comprising: (d) after (c), removing (i) at least a portion of the dopant-containing film, or (ii) at least a portion of the capping film, or (iii) at least a portion of the dopant-containing film and at least a portion of the capping film from the semiconductor substrate.
 3. The method of claim 1, wherein the channel region is fin-shaped, and the dopant-containing film substantially conforms to the shape of the fin-shaped channel region.
 4. The method of claim 1, wherein the channel region is fin-shaped, and the driving in (c) comprises a thermal anneal which enhances diffusion of the dopant from the dopant-containing film to the fin-shaped channel region.
 5. The method of claim 1, wherein the dopant is boron.
 6. The method of claim 5, wherein at least some of the multiple dopant-containing layers comprise a borosilicate glass.
 7. The method of claim 6, wherein the dopant-containing film precursor is an alkyl borate.
 8. The method of claim 7, wherein the alkyl borate is trimethyl borate.
 9. The method of claim 1, wherein the dopant is phosphorous.
 10. The method of claim 1, wherein the dopant is arsenic.
 11. The method of claim 1, wherein the reacting in (a)(iii) comprises contacting the adsorbed dopant-containing film precursor with a plasma.
 12. The method of claim 1, wherein the reacting in (a)(iii) comprises reacting the adsorbed dopant-containing film precursor with another reactive chemical species which may or may not be first adsorbed onto the semiconductor substrate.
 13. The method of claim 1, wherein forming the capping film comprises a chemical vapor deposition process.
 14. The method of claim 13, wherein the chemical vapor deposition process is plasma enhanced.
 15. The method of claim 1, wherein forming the capping film comprises an atomic layer deposition process.
 16. The method of claim 1, wherein the channel region is fin-shaped having a width of less than about 12 nanometers.
 17. The method of claim 1, wherein an average thickness of the capping film is between about 10 and 100 Angstroms.
 18. The method of claim 1, wherein a relative standard deviation in thickness of the capping film is less than about 10%.
 19. The method of claim 1, wherein an average concentration of the silicon nitride in the capping film is between about 2 and 3 g/cm³.
 20. The method of claim 1, wherein at least some of the multiple substantially dopant-free layers comprise a dielectric material and the capping film comprises a dielectric material different than said dielectric material of the at least some of the multiple substantially dopant-free layers.
 21. The method of claim 20, wherein said dielectric material of the at least some of the multiple substantially dopant-free layers is a silicon dioxide.
 22. The method of claim 1, wherein in (a): a second dopant-rich portion of the dopant-containing film is formed by depositing the multiple dopant-containing layers in (i) through (v) sequentially, without intervening deposition of a substantially dopant-free layer; and a second substantially dopant-free portion of the dopant-containing film is formed by depositing the multiple substantially dopant-free layers in (vi) through (x) sequentially, without intervening deposition of a dopant-containing layer; and wherein the first dopant-rich portion, the first substantially dopant-free portion, the second dopant-rich portion, and the second substantially dopant-free portion of the dopant-containing film are deposited in the following sequence: first dopant-rich portion, then first substantially dopant-free portion, then second dopant-rich portion, then second substantially dopant-free portion. 